Explicit check for Python 3.10 in Windows

[densnow]

If the instruction to install Python 3.10 is missed or ignored on a windows installation, it might not be obvious to the user (and anyone helping with troubleshooting) what the problem is. The lines "Downloading and installing M269 files..." and all that follows, plus the line "Creating Python environment $VENV... (this will take a bit)" will still be printed if user does not have Python 3.10 (As far as I can tell)

In the Unix install script we have an explicit check for Python 3.10 with a clear message and exit. Is it worth having something similar in the windows script?

[densnow]

So it looks like a py -3.10 ... command will default to another (possibly latest) version if 3.10 cannot be found. The only way the script would become messy is if Python was not installed at all.

[densnow]

I think this issue will be handled when #28 is dealt with, so probably should be closed?

[mwermelinger]

I think these are separate issues: the activation may fail in spite of 3.10, or may succeed in spite of 3.11, so best to check both separately.